Dual cassette load lock

ABSTRACT

A workpiece loading interface is included within a workpiece processing system which processes workpieces, typically wafers, in a vacuum. The workpiece loading interface includes two separate chambers. Each chamber may be separately pumped down. Thus, while a first cassette of wafers, from a first chamber is being accessed, a second cassette of wafers may be loaded in the second chamber and the second chamber pumped down. Each chamber is designed to minimize intrusion to a clean room. Thus a door to each chamber has a mechanism which, when opening the door, first moves the door slightly away from an opening in the chamber and then the door is moved down parallel to the chamber. After the door is opened, a cassette of wafers is lowered through the opening in a motion much like a drawbridge. The cassette may be pivoted within the chamber when the position from which wafers are accessed from the cassette differs from the position from which the cassette is lowered out of the chamber.

BACKGROUND

The present invention relates to a front end loading interface used inthe loading of workpieces in semiconductor processing equipment.

Semiconductor processing equipment often has a plurality of chambers inwhich processing occurs. Arm assemblies or other robotic devices aregenerally used to move workpieces, generally wafers, from a waferqueuing station to various chambers for processing. When the processingis finished the wafer is returned to the queuing station. For an exampleof prior art processing equipment, see U.S. Pat. No. 4,715,921 issued toMaher et al. for a Quad Processor.

Semiconductor processing is typically done in a vacuum. Therefore, awafer queuing station into which is placed a cassette of wafers to beprocessed must be pumped down before the wafers may be accessed. Thissignificantly increases the time the semiconductor processing equipmentis idle while waiting for a cassette of processed wafers to be exchangedfor a cassette of unprocessed wafers and for subsequent pumping down ofthe wafer queuing station.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiment of the present invention, aworkpiece loading interface is presented for inclusion within aworkpiece processing system. The workpiece loading interface includestwo separate chambers. Each chamber may be separately pumped down. Thus,while a first cassette of workpieces, typically wafers, from a firstchamber are being accessed, a second cassette of wafers may be loaded inthe second chamber and the second chamber may then be pumped down. Thiscan significantly increase throughput of wafers through the workpieceprocessing system.

In the preferred embodiment, each chamber is designed to minimizeintrusion to a clean room. Thus a door to each chamber has a mechanismwhich, when opening the door, first moves the door slightly away from anopening in the chamber and then the door is moved down parallel to thechamber. After the door is opened, a cassette of wafers is loweredthrough the opening in a motion much like a drawbridge. The cassette ofwafers is on a support with no side panels, facilitating the replacementof a cassette of processed wafers with a cassette of unprocessed wafersby an automated device. The cassette may be pivoted within the chamberwhen the position from which wafers are accessed from the cassettediffers from their position when the cassette is lowered out of thechamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a block diagram of semiconductor processingequipment which includes two cassette load locks in accordance with thepreferred embodiment of the present invention.

FIG. 2 shows a block diagram of a load lock which is part of thesemiconductor processing equipment shown in FIG. 1 in accordance withthe preferred embodiment of the present invention.

FIG. 3 shows a second block diagram of the load lock shown in FIG. 2 inaccordance with the preferred embodiment of the present invention.

FIG. 4 shows another block diagram of the load lock shown in FIG. 2 inaccordance with the preferred embodiment of the present invention.

FIG. 5 is a block diagram of a cassette wafer holder in a positionextended out of the load lock shown in FIG. 2 in accordance with thepreferred embodiment of the present invention.

FIG. 6 is a block diagram of the cassette wafer shown in FIG. 5 in anupright position within the load lock shown in FIG. 2 in accordance withthe preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a top view of semiconductor processing equipment 1 is shown.Semiconductor processing equipment 1 may be used, for example, foretching wafers.

Semiconductor processing equipment 1, includes, for example, aprocessing chamber 3, a processing chamber 4, a processing chamber 5 anda processing chamber 6. A central chamber 2 may be used to temporarilystore wafers on robotic equipment 7 when wafers are being moved to orfrom various of the processing chambers.

Semiconductor processing equipment 1 also includes dual cassette loadlocks. In chamber 8, a wafer cassette 16 holds wafers 10. In chamber 9,a wafer cassette 17 holds wafers 11. Wafer cassette 17 pivots around apivot point 15. When wafers 11 from cassette 17 are accessed bysemiconductor processing equipment 1 for processing, wafer cassette 17is flush against a gate 13, as shown, and easily accessed by roboticequipment 7 for transportation into central chamber 2. When wafercassette 17 is ready to be removed from chamber 9, wafer cassette 17 ispivoted back from gate 13 in preparation for the opening of chamber 9and removal of wafer cassette 17.

Similarly, wafer cassette 16 pivots around a pivot point 14. When wafers10 from cassette 16 are accessed by semiconductor processing equipment 1for processing, wafer cassette 16 is flush against a gate 12 and easilyaccessed by robotic equipment 7 for transportation into central chamber2. When wafer cassette 16 is ready to be removed from chamber 8, wafercassette 16 may be pivoted back an angle 18 from gate 12, as shown, inpreparation for the opening of chamber 8 and removal of wafer cassette16. In the preferred embodiment, angle 18 is about twenty-one degrees.

Chamber 8 and chamber 9 may be separately and individually pumped down.A vacuum pump 19 is able to provide a vacuum in chamber 8. A vacuum pump20 is able to provide a vacuum in chamber 9. In FIG. 1, vacuum pumps 19and 20 are shown in schematic form. Typically pumps 19 and 20 wouldreside within semiconductor processing equipment 1. Further, while FIG.1 shows two separate pumps, a single pump could be used to separatelyand individually pump down chamber 8 and chamber 9.

FIG. 2 shows a simplified block diagram front view of wafer chamber 8.In the preferred embodiment, the volume of chamber 8 is 46 liters. Adoor 21 is shown in a closed position. Door 21 includes an observationwindow 22. Door 21 is opened and closed using a pneumatic actuatorwithin a rod 24. Magnets in the pneumatic actuator interface attract anouter ring 26. Outer ring 26 is connected to door 21 through an assembly23.

FIG. 3 shows door 21 lowered into an open position. An opening 25, forexample may be fifteen inches high and ten and one half inches wide. Byopening down, the intrusion of door 21 into a clean room may beminimized. In the preferred embodiment the total intrusion is about oneinch.

Once door 21 is lowered, wafer cassette 16, on a support structure 43,may then be lowered out of chamber 8, much like a draw bridge is loweredat a castle entrance. Wafer cassette 16 may then be removed and a newwafer cassette placed upon support structure 43. Support structure 43 isdesigned with a open bottom so that when door 21 is opened and wafercassette 16 is lowered, a laminar airflow may sweep downward throughwafers 10.

In FIG. 4, additional detail of the mechanism which controls the openingand shutting of the door 21 is shown. A side panel 31 of door 21 isconnected to a carriage 30 by a spring 34, a link 36 and a link 35. Ascontrolled by the pneumatic actuator within rod 24, door 21 travels upand down parallel to a rail 50. When being closed, door 21 is stopped byan abutment 32; however, carriage 30 continues upward, expanding spring34, until a gap 33 is completely closed. While carriage 30 continuesmoving upward, a pivot 39 connected to link 36, and a pivot 40 connectedto link 35 continue moving upward. However a pivot 37 connected to link36 and a pivot 38 connected to link 35 cause door 21 to move towardscarriage 30. Therefore, as gap 33 is closed, links 35 and 36 translatethe upward motion of carriage 30 into horizontal motion of door 21. Door21 is thus brought snug against, and hence seals chamber 8.

When door 21 is opened, spring 34 compresses causing gap 33 to reappearand links 35 and 36 to straighten, thus moving door 21 horizontally awayfrom chamber 8.

FIGS. 5 and 6 show a block diagram of one possible implementation of anassembly for guiding the lowering and raising of support structure 43.In FIG. 5, support structure 43 and cassette 16 are shown lowered out ofchamber 8. A roller 44 connected to support structure 43 is shownresting on an extension of a cam containing slot 46 within chamber 8. Aroller 45, also connected to support structure 43, is shown at a firstend of a slot track 46.

In FIG. 6, support structure 43 and cassette 16 are shown in the uprightposition within chamber 8. In this position, wafers 10 are horizontaland are stacked so that they are ready to be accessed by semiconductorprocessing equipment 1. When support structure 43 and cassette 16 are inthe upright position, roller 45 is rolled to a second end of slot track46 and roller 44 rests against a stop 49. Stop 49 is an extension of thecam which contains slot 46.

We claim:
 1. In a workpiece processing system comprising multiple vacuumchambers connected to a central chamber, a workpiece loading interfacecomprising:dual external chambers each having an opening for receivingworkpieces held in a cassette and for forwarding the workpieces to thecentral chamber of the workpiece processing system for processing;cassette support means for lowering the cassette of workpieces out ofeach of said external chambers through said opening in a drawbridgemotion; means for producing a vacuum in each of said dual externalchambers and pivot means within each dual external chamber for pivotingthe cassette support between a first position accessing said opening,and a second position from which workpieces from the cassette may beaccessed by the central chamber of the workpiece processing system.
 2. Aworkpiece processing system as in claim 1 wherein each of the dualexternal chambers include:a door which, when shut, covers and seals theopening; and means for opening said door by first moving the doorparallel to the chamber to expose said opening.
 3. A workpieceprocessing system as in claim 1 wherein said cassette is transferredinto and out of said external chambers on a support having an openbottom.